A Redox-Reconfigurable,
Ambidextrous Asymmetric Catalyst
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Abstract
A redox-reconfigurable catalyst derived from l-methionine
and incorporating catalytic urea groups has been synthesized. This
copper complex catalyzes the enantioselective addition of diethyl
malonate to <i>trans</i>-β-nitrostyrene. Either enantiomer
of the product can be predetermined by selection of the oxidation
state of the copper ion. Enantiomeric excesses of up to 72% (S) and
70% (R) were obtained in acetonitrile. The ability of the catalyst
to invert enantiomeric preference was reproduced with several different
solvents and bases. Facile interconversion between the Cu<sup>2+</sup> and Cu<sup>+</sup> redox states allowed easy access to both active
helical forms of the complex and, therefore, dial-in enantioselectivity